Beneficial culture powders and in particular probiotic culture powders are added to a wide range of shelf-stable products. Most low moisture products containing probiotic culture powders claim a shelf-life of at least 18 months. During this period, a minimum amount of live microbes must be guaranteed in the product. For this reason, the dosage of culture powder in the product needs to account for the loss in microbial viability during storage. It is therefore important to find ways of protecting microorganisms during processing and during storage to promote their survival.
Bacteria experience various stresses during drying under warm conditions, such as heat and shear stress in the dryer or osmotic stress due to dehydration, for example during spray-drying. These stresses can have detrimental or even lethal effects on the bacteria. By addition of protective agents, the bacteria can be stabilized to a certain degree against these stresses. Further stress is applied on the bacteria during storage. Also, when the powder is reconstituted with liquid, the bacteria are exposed to osmotic stress.
Protective agents can stabilize microorganisms during drying, storage and/or reconstitution. A protective effect during drying mostly comes along with a stabilizing effect during storage and reconstitution, because when microorganisms are better protected during drying, they are less injured and, as a consequence, more robust during storage and reconstitution.
Numerous ingredients have been suggested in literature as protective agents. For example, JP3504365 describes a protective agent for freeze-drying of bacteria comprising a mixture of at least three ingredients selected from aspartic acid, arginine, glutamic acid, proline, lysine, leucine and methionine. However, freeze-drying and drying processes using warm gas, such as spray-drying, are very different in nature and expose the biomass to different stress factors. Therefore disclosed protective agents for freeze-drying processes are of no help to identify protective agents suitable to protect microorganisms such as bacteria during a drying process using a warm gas, such as spray-drying, and subsequent storage and reconstitution.
Some documents relate specifically to the spray-drying of microorganisms. For example EP1281752 B1 describes a method of spray-drying microbial cells. Focus is on the size of the powder particles obtained and on the low temperature used for the drying process. This document also states that a protective agent commonly known in the art can be used. It provides numerous examples of potential protective agents, namely vitamins such as ascorbic acid; amino acids such as glutamine, glutamic acid, cysteine, glycine, phenylalanine, serine or threonine; saccharides or sugar alcohols such as glucose, fructose, sucrose, maltose, mannitol or maltitol; polysaccharides such as oligosaccharides, cyclodextrin or dextrin; fats such as higher fatty acids obtained from rapeseed, soybean, peanut, etc.; proteins such as those obtained from cow's milk, soybean, etc. and degraded proteins such as peptides; inorganic salts such as magnesium sulphate; and others such as sucrose fatty acid ester, malic acid, nucleic acids, yeast extract, skim milk, peptone, gelatin, tannin, etc. These ingredients can be used alone or in any combination thereof. This document does not provide any guidance with regards to selection of particular combinations of ingredients having optimal activity.
Similarly U.S. Pat. No. 6,010,725 relates to spray-drying of microorganisms and their survival. Its teaching is focused on the conditions to be applied during the spray-drying process. It also states that a variety of protective agents known in the literature can be used and recites as examples ascorbic acid, amino acids and their salts such as lysine, cysteine, glycine and sodium glutamate, proteins or protein hydrolysates, sugars such as lactose, trehalose, sucrose, dextrin and maltodextrin, and fats.
Despite the numerous disclosures of abundant lists of ingredients of potential use as protective agents, there is a need for further refinement and identification of combinations of ingredients having optimized activity to protect microorganisms during drying processes using warm gas and along subsequent storage and reconstitution.
The present invention advantageously solves the above-mentioned problems.